Shrink wrapping is well known as an efficient and low cost manner of encasing articles in a plastic overwrap. Shrink wrap material typically comprises a thin plastic extruded film which is placed under tension and stretched while still hot, and maintained under tension while cooled to ambient temperature. While maintained at ambient temperature, the film retains its stretched dimensions. When heat is re-applied to the film, it returns to its original size. To encase articles in a plastic overwrap, the articles are wrapped in plastic shrink wrap material and passed through a heat tunnel, whereupon the shrink wrap material shrinks and pulls tightly about the articles. Upon subsequent cooling to ambient temperature again, the shrink wrap material retains its shrunken dimensions and remains tightly wrapped about the articles. Thus, the shrink wrap material holds the articles together and provides protection of the articles from weather and the like during shipping.
Shrink wrapping material generally conforms smoothly about the exterior surfaces of the wrapped articles. However, it has been found that the shrink wrap material wrinkles over exterior surface portions of the articles having spaces or gaps. Such wrinkling of the shrink wrap material which occurs over gaps or spaces of the articles is generally acceptable for shipping purposes, wherein the aesthetics of the wrapped articles are not particularly important. However, in consumer products it is important that the product package have a good aesthetic appearance. Hence, there is a need for a shrink wrapped package for use in packaging consumer products in which the shrink wrap material extends substantially unwrinkled over the packaged articles, including spaces or gaps in the articles.
More particularly, in the shrink wrapping of a stack of containers, such as microwavable food containers, wherein each of the containers has inwardly sloped sides and a cover which extends outwardly beyond the sloped sides of the respective container, the shrink wrap material tends to wrinkle considerably in the space below the outwardly extending cover of the bottom container. That is, the outward extension of each cover, and the inwardly sloped walls of each of the containers beneath their respective covers, forms a space or gap between the container walls and the peripheries of the covers, over which space the shrink wrap material extends without support. The lack of support for the shrink wrap material over these spaces causes the shrink wrap material to wrinkle in the space. Accordingly, there is a need for a shrink wrapped package having a plurality of stacked containers, each with sloped sides and enlarged cover, which does not have significant wrinkling.
A paperboard sleeve has been used to surround the stack of containers and thereby provide support for the shrink wrap material about the periphery of the stack of containers sufficient to reduce wrinkling. However, at the lower end of the sleeve, where the sidewalls of the lowermost container of the stack slopes inwardly beneath the overhanging cover, the sleeve end is spaced from the sidewall of the lowermost container and there is no support for the sleeve. Hence, upon shrinkage of shrink wrap material about the sleeve, the inward force exerted by the shrink wrap material warps or bends the lower end of the sleeve inwardly, resulting in an aesthetically inferior product. Accordingly, there is a need for packaging suitable for encasing a stack of containers in shrinkable material which provides a shrink wrapped package having good aesthetic appearance, without significant warpage or wrinkling.
Still further, the shrink wrap material is frequently torn or punctured by the sharp corners of the stack of articles and there is a need for a shrink wrapped package which substantially reduces puncturing or tearing of the corners of the package.